Globally planarized backend compatible thin film resistor contact/interconnect process

ABSTRACT

A method of forming a thin film resistor contact incorporates an etch-stop material to protect the underlying thin film resistor from a subsequent dry etching process to form a contact opening to the thin film resistor. More specifically, the method includes forming a thin film resistor, forming a first dielectric layer over the thin film resistor, forming a first opening through the first dielectric layer to expose an underlying portion of the thin film resistor, forming an etch-stop within the first opening of the first dielectric layer, forming a second dielectric layer over the etch-stop and the first dielectric layer, forming a second opening through the second dielectric layer to expose the underlying portion of the etch-stop, and forming a metal plug within the second contact opening, wherein the metal plug is in electrical contact with the thin film resistor by way of the etch-stop. Alternatively, in the case of an insulating etch-stop, the second opening through the dielectric layer is through the etch-stop, and forming a metal plug within the second contact opening, wherein the metal plug is in direct electrical contact with the thin film resistor.

FIELD OF THE INVENTION

This invention relates generally to semiconductor processing, and inparticular, to a method of forming a thin film resistor contact.

BACKGROUND OF THE INVENTION

Thin film resistors are employed in many integrated circuits. Thin filmresistors are used in integrated circuits to implement the desiredfunctionality of the circuit, including biasing of active devices,serving as voltage dividers, assisting in impedance matching, etc. Theyare typically formed by deposition of a resistive material on adielectric layer, and subsequently patterned to a desired size andshape. Often, a thin film resistor is subjected to a heat treatmentprocess (i.e. annealing) to improve its stability and to bring theresistance to a desired value.

Generally, after all the thin film resistors and other components of anintegrated circuit are formed, a dielectric layer is deposited toinsulate the resistors and other components from the interconnectwiring. This dielectric layer may be subjected to planarization bychemical-mechanical polishing (CMP) if reduced topography is desiredbefore forming the interconnect wiring. Once the dielectric layer isformed, contacts are made through the layer to make electricalconnections to thin film resistors and other components of theintegrated circuit.

To minimize any perturbation to the thin film resistors, these contactsneed to be etched with a process that is highly selective to the thinfilm resistor material. Under this requirement, an optimal wet etchprocess is more readily achievable than a dry etch process and hencepreferred. Once the contact openings are made, a metal plug processcould be used to establish the electrical contact between the thin filmresistor and the subsequent interconnect wiring. The metal plug processcould be done with deposition of a barrier metal stack followed bytungsten, aluminum, and/or copper deposition. In a planarized backendprocess where the dielectric above the thin film is polished to achieveflatness, the preferred method for the metal plug process furtherinvolves polishing or etch-back of the metal-plug material following itsdeposition.

A problem with forming contacts to thin film resistors arises from thefact that the dielectric above the thin film resistors has a thicknessvariation stemming from natural process and process equipmentvariations. If this dielectric is polished, as described above, thisthickness variation is further exacerbated due to the additionalvariation produced by the polish process. Thus, the thin film resistorsacross a wafer or from wafer-to-wafer can be at different depths belowthe top surface of the dielectric layer.

Because of the different depths of the thin film resistors, the etchingof the contact openings has to be conducted in a manner that guaranteescontact opening to the deepest thin film resistor and/or component. As aconsequence, the contact openings for shallower thin film resistors areoveretched. As such, controlled dry etching may be more difficult toachieve since degradation and/or punch-through of the shallower thinfilm resistors is highly probable. In the case of wet etching, all thinfilm contacts are wider due to the isotropic nature of wet etching.Moreover, the shallower thin film resistor contacts would be furtherenlarged because of overetching. When metal plugs are used following theformation of wet-etched contacts, the wide contact openings lead toincomplete fill. Furthermore, when tungsten is used as the plugmaterial, poor plug adhesion due to stress and excessive removal of theplug due to tungsten polish could result.

To circumvent the above problem, the dielectric below the thin filmresistors could be planarized by chemical-mechanical polishing prior todepositing and patterning the thin film resistors. Consequently,topography created by other components of an integrated circuit areglobally planarized. As the addition of thin film resistors typicallyadds little topography, this method obviates the need for planarizationof the dielectric deposited above thin film resistors. But while itreduces the problem of dielectric non-uniformity above the thin filmresistors, the increase in dielectric non-uniformity below the thin filmresistors makes it difficult to employ laser-trimming of individualresistors when high precision resistance values are required. This isbecause the dielectric thickness below the thin film resistors modulatesthe laser irradiation requirements for trimming.

Thus, there is a need for a method of forming a thin film resistorcontact which eliminates or reduces the drawbacks associated with theprior art method of forming thin film resistor contacts. Such a methodand resulting contact is disclosed herein in accordance with theinvention.

SUMMARY OF THE INVENTION

An aspect of the invention relates to a new and improved method offorming a thin film resistor contact. With this new and improved method,the above issues associated with dry or wet etching of the contactopenings to thin film are eliminated. Also, with this new and improvedmethod, the underlying thin film resistors are protected from thecustomary etching process used to make the contact openings. In summary,the new and improved method of forming a thin film resistor contactincorporates an etch-stop material to protect the underlying thin filmresistor from a subsequent process of dry etching the contact opening tothe thin film resistor. The dry etching of the contact openings allowsmore control over the size of the openings, which then makes metal plugprocesses more manufacturable and reliable.

More specifically, the method of forming a thin film resistor contact ofthe invention comprises the steps of forming a thin film resistor,forming a first dielectric layer over the thin film resistor, forming afirst opening through the first dielectric layer to expose an underlyingportion of the thin film resistor, forming an electrically conductiveetch-stop within the first opening of the first dielectric layer,forming a second dielectric layer over the etch-stop and the firstdielectric layer, forming a second opening through the second dielectriclayer to expose the underlying portion of the etch-stop, and forming ametal plug within the second contact opening, wherein the metal plug isin electrical contact with the thin film resistor by way of theetch-stop.

Another method of forming a thin film resistor contact of the inventioncomprises the steps of forming a thin film resistor, forming a firstdielectric layer over the thin film resistor, forming a first openingthrough the first dielectric layer to expose an underlying portion ofthe thin film resistor, forming an electrically conductive etch-stopwithin the first opening of the first dielectric layer and continuouslyover another region of the first dielectric layer that does not overliethe thin film resistor, forming a second dielectric layer over theetch-stop and the first dielectric layer, forming a second openingthrough the second dielectric layer to expose the underlying region ofthe etch-stop that is not situated over the thin film resistor, andforming a metal plug within the second contact opening, wherein themetal plug is in electrical contact with the thin film resistor by wayof the etch-stop.

In the exemplary implementation of the above methods of forming a thinfilm resistor contact, the electrically conductive etch-stop can becomprised of a combination of titanium and titanium-nitride, ortitanium-tungsten and titanium-tungsten-nitride, or other suitablematerial that is electrically conductive and relatively selective to dryetching processes.

Yet another alternative method of forming a thin film resistor contactof the invention comprises the steps of forming a thin film resistor,forming a first dielectric layer over the thin film resistor, forming afirst opening through the first dielectric layer to expose an underlyingportion of the thin film resistor, forming an electrically insulatingetch-stop within the first opening of the first dielectric layer,forming a second dielectric layer over the etch-stop and the firstdielectric layer, forming a second opening through the second dielectriclayer to expose the underlying portion of the etch-stop, removing theetch-stop to expose the underlying thin film resistor, and forming ametal plug within the second contact opening, wherein the metal plug isin direct electrical contact with the thin film resistor.

Still another alternative method of forming a thin film resistor contactof the invention comprises forming a thin film resistor; forming anelectrically insulating etch-stop layer over the thin film resistor;forming a dielectric layer over the etch-stop layer; forming a firstopening through the dielectric layer to expose a first underlying regionof the etch-stop layer; forming a second opening through the insulatingetch-stop layer to expose a second underlying region of the thin filmresistor; and forming a metal plug within the first and second openings,wherein the metal plug is in direct electrical contact with the thinfilm resistor.

In the exemplary implementation of the above alternative methods offorming a thin film resistor contact, the electrically insulatingetch-stop can be comprised of a silicon oxynitride, silicon nitride, orother suitable material that is electrically insulating but isrelatively selective to dry etching processes.

Other aspects of the invention relate to the resulting thin filmresistor contact made by the method of the invention. Additionally,other aspects, features and techniques of the invention will becomeapparent to one skilled in the relevant art in view of the followingdetailed description of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a cross-sectional view of an exemplary semiconductordevice at an initial stage of a method of forming a thin film resistorcontact in accordance with the invention;

FIG. 2 illustrates a cross-sectional view of the exemplary semiconductordevice at a subsequent step of the method of forming a thin filmresistor contact in accordance with the invention;

FIG. 3 illustrates a cross-sectional view of the exemplary semiconductordevice at a subsequent step of the method of forming a thin filmresistor contact in accordance with the invention;

FIG. 4 illustrates a cross-sectional view of the exemplary semiconductordevice at a subsequent step of the method of forming a thin filmresistor contact in accordance with the invention;

FIG. 5 illustrates a cross-sectional view of the exemplary semiconductordevice at a subsequent step of the method of forming a thin filmresistor contact in accordance with the invention;

FIG. 6 illustrates a cross-sectional view of the exemplary semiconductordevice at a subsequent step of the method of forming a thin filmresistor contact in accordance with the invention;

FIG. 7 illustrates a cross-sectional view of the exemplary semiconductordevice at a subsequent step of the method of forming a thin filmresistor contact in accordance with the invention;

FIG. 8 illustrates a cross-sectional view of the exemplary semiconductordevice at a subsequent step of the method of forming a thin filmresistor contact in accordance with the invention;

FIG. 9 illustrates a cross-sectional view of the exemplary semiconductordevice at a subsequent step of the method of forming a thin filmresistor contact in accordance with the invention;

FIG. 10 illustrates a cross-sectional view of the exemplarysemiconductor device at a subsequent step of the method of forming athin film resistor contact in accordance with the invention;

FIG. 11A illustrates a cross-sectional view of the exemplarysemiconductor device at a subsequent step of the method of forming athin film resistor contact in accordance with the invention;

FIG. 11B illustrates a cross-sectional view of the exemplarysemiconductor device at a subsequent step of an alternative method offorming a thin film resistor contact in accordance with the invention;

FIG. 12 illustrates a cross-sectional view of an exemplary semiconductordevice at a step of a first alternative method of forming a thin filmresistor contact in accordance with the invention;

FIG. 13 illustrates a cross-sectional view of an exemplary semiconductordevice at a step of a second alternative method of forming a thin filmresistor contact in accordance with the invention;

FIG. 14 illustrates a cross-sectional view of an exemplary semiconductordevice at a step of a third alternative method of forming a thin filmresistor contact in accordance with the invention;

FIG. 15 illustrates a cross-sectional view of an exemplary semiconductordevice at a subsequent step of a third alternative method of forming athin film resistor contact in accordance with the invention; and

FIG. 16 illustrates a cross-sectional view of an exemplary semiconductordevice after subsequent steps of a third alternative method of forming athin film resistor contact in accordance with the invention;

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates a cross-sectional view of an exemplary semiconductordevice 100 at an initial stage of a method of forming a thin filmresistor contact in accordance with the invention. At this step, thesemiconductor device 100 comprises a substrate 102 and a firstdielectric layer (e.g. silicon dioxide (SiO₂)) 104 disposed over thesubstrate 102. The semiconductor device 100 at this initial stage is anexample of what a semiconductor device may be comprised of prior to theformation of the thin film resistor and its contact in accordance withthe invention. It shall be understood that the semiconductor device 100at this stage may have a different appearance.

FIG. 2 illustrates a cross-sectional view of the exemplary semiconductordevice 100 at a subsequent step of the method of forming a thin filmresistor contact in accordance with the invention. At this subsequentstep, a layer of thin film resistor material 106 is formed over thefirst dielectric layer 104, and then a mask layer 108 is formed over thethin film resistor material 106. The thin film resistor material 106 maybe comprised of silicon chromium (SiCr), nickel chromium (NiCr),tantalum nitride (TaN), and/or other suitable resistor materials.

FIG. 3 illustrates a cross-sectional view of the exemplary semiconductordevice 100 at another subsequent step of the method of forming a thinfilm resistor contact in accordance with the invention. At thissubsequent step, the mask layer 108 is developed and patterned to form amask 108′ that defines the underlying thin film resistor.

FIG. 4 illustrates a cross-sectional view of the exemplary semiconductordevice 100 at another subsequent step of the method of forming a thinfilm resistor contact in accordance with the invention. At thissubsequent step, the thin film resistor material 106 is etched offexcept that portion which underlies the mask 108′. This forms a thinfilm resistor 106′. In this example, only the contact region of the thinfilm resistor 106′ is shown in order to illustrate the method of forminga thin film resistor contact in accordance with the invention. The thinfilm resistor material 106 may be etched using anisotropic or isotropicetching techniques.

FIG. 5 illustrates a cross-sectional view of the exemplary semiconductordevice 100 at another subsequent step of the method of forming a thinfilm resistor contact in accordance with the invention. At thissubsequent step, the mask 108′ is removed. Then, a second dielectriclayer (e.g. a layer of silicon dioxide (SiO₂)) 110 is formed over thethin film resistor 106′ and over the exposed portion of the firstdielectric layer 104. And, a mask layer 112 is formed over the seconddielectric layer 110. In the exemplary implementation of the method ofthe invention, the second dielectric layer 110 is deposited to athickness ranging from about few hundred Angstroms to a few thousandAngstroms. The mask layer 112 may be a photo resist or other materialthat can serve as a mask layer.

FIG. 6 illustrates a cross-sectional view of the exemplary semiconductordevice 100 at another subsequent step of the method of forming a thinfilm resistor contact in accordance with the invention. At thissubsequent step, the mask layer 112 is developed and patterned to form amask 112′ having an opening 114 that defines the underlying contactopening for the thin film resistor 106′. Then, the second dielectriclayer 110 is etched off at a portion underlying the opening 114 of themask 112′ to form contact opening for the thin film resistor 106′. Theremoval of layer 110 at a portion underlying the opening 114 ispreferably accomplished by wet-etching, though dry-etching may beavailable to one skilled in the relevant art. The remaining seconddielectric layer 110′ serves to passivate the thin film resistor 106′ atthe non-contacted portion of the resistor 106′.

FIG. 7 illustrates a cross-sectional view of the exemplary semiconductordevice 100 at another subsequent step of the method of forming a thinfilm resistor contact in accordance with the invention. At thissubsequent step, an etch-stop material layer 116 is formed over theportion of the thin film resistor 106′ underlying the contact openingand over the remaining second dielectric layer 110′. Then, a mask layer120 is formed over the etch-stop material layer 116. In the exemplaryimplementation of the method of the invention, the etch-stop materiallayer 116 may be comprised of an electrical conductor, such as titaniumand titanium-nitride (Ti/TiN), and/or a titanium-tungsten (TiW) andtitanium-tungsten-nitride (TiWN), or any other electrically conductivematerial that is selective to a subsequent dry etching process.Alternatively, the etch-stop material layer may be comprised of anelectrical insulator, such as silicon oxynitride, silicon nitride, orother suitable material that is electrically insulating and relativelyselective to dry etching processes. The mask layer 120 may be a photoresist or other material that can serve as a mask layer.

FIG. 8 illustrates a cross-sectional view of the exemplary semiconductordevice 100 at another subsequent step of the method of forming a thinfilm resistor contact in accordance with the invention. At thissubsequent step, the mask layer 120 is developed and patterned to form amask 120′ which defines the underlying etch-stop region of the etch-stopmaterial layer 116. Then, the etch-stop material layer 116 is etched offexcept that portion underlying the mask 120′. This forms an etch-stop116′ disposed over the thin film resistor 106′ within the contactopening of the second dielectric layer 110′ and also above the region ofthe second dielectric layer 110′ proximate the contact opening. In theexemplary implementation of the method of the invention, the etching ofthe etch-stop material layer 116 can be performed by anisotropic orisotropic etching techniques.

FIG. 9 illustrates a cross-sectional view of the exemplary semiconductordevice 100 at another subsequent step of the method of forming a thinfilm resistor contact in accordance with the invention. At thissubsequent step, the mask 120′ is stripped off. Then, a dielectric layer122 is deposited over the etch-stop 116′ and over the exposed portionsof the second dielectric layer 110′. After the dielectric layer 122 hasbeen deposited, it may be polished to achieve a desired planarizationfor its top surface and a desired thickness. In the exemplaryimplementation of the method of the invention, the dielectric layer 122may be comprised of deposited silicon dioxide (SiO₂) and the polishingof the dielectric layer 122 may be performed by chemical mechanicalpolishing (CMP).

FIG. 10 illustrates a cross-sectional view of the exemplarysemiconductor device 100 at another subsequent step of the method offorming a thin film resistor contact in accordance with the invention.At this subsequent step, a contact opening 124 is formed through thedielectric layer 122 to expose the underlying etch-stop 116′. This stepis performed by forming a mask layer (not shown) over the dielectriclayer 122, developing and patterning the mask layer to form an openingabove the to-be formed contact opening, and then dry etching thedielectric layer 122 through the opening of the mask to form the contactopening 124′. The remaining dielectric layer 122′ serves to insulate theunderlying structures of the semiconductor device 100 from theinterconnect wiring to be formed over the dielectric layer 122′.

FIG. 11A illustrates a cross-sectional view of the exemplarysemiconductor device 100 at another subsequent step of the method offorming a thin film resistor contact in accordance with the invention.In this case, the etch-stop material 116′ is electrically conductive. Atthis step, a metal plug 126 is formed within the contact opening 124′ ofthe dielectric layer 122′. In the exemplary implementation of the methodof the invention, the metal plug 126 is formed by sequentiallydepositing a barrier layer (Ti/TiN) and tungsten (W) to fill the contactopening 124′. Then, the tungsten material is etched or polished back toremove the tungsten (W) off the top surface of the dielectric layer122′. The tungsten plug 126 makes electrical contact to the thin filmresistor 106′ by way of the electrically conductive etch-stop 116′.

FIG. 11B illustrates a cross-sectional view of an exemplarysemiconductor device 100′ at another step (subsequent to the deviceshown in FIG. 10) of a first alternative method of forming a thin filmresistor contact in accordance with the invention. In this case, theetch-stop material 116″ is electrically insulating. At this step, thecontact opening 124′ is partially formed by etching of the dielectriclayer 122′ using a process that is selective to the etch-stop material116″. Subsequently, the portion of the etch-stop material 116″ thatunderlies the contact opening 124′ is removed using a process that isselective to the thin film resistor 106′. This process could result inan etch-stop spacer 116″ being formed around the perimeter of thecontact opening.

FIG. 12 illustrates a cross-sectional view of the exemplarysemiconductor device 100′ at another subsequent step of the firstalternative method of forming a thin film resistor contact in accordancewith the invention. At this step, a metal plug 128 is formed within thecontact opening 124′ of the dielectric layer 122′. In the exemplaryimplementation of the method of the invention, the metal plug 128 isformed by sequentially depositing a barrier layer (Ti/TiN) and tungsten(W) to fill the contact opening 124′. Then, the tungsten material isetched or polished back to remove the tungsten (W) off the top surfaceof the dielectric layer 122′. The tungsten plug 128 makes directelectrical contact to the thin film resistor 106′, as opposed to anindirect electrical contact to the thin film resistor 106′ as is thecase when the etch-stop is electrically conductive.

FIG. 13 illustrates a cross-sectional view of an exemplary semiconductordevice 100″ at a step of a second alternative method of forming a thinfilm resistor contact in accordance with the invention. In this secondalternative method, the electrically conductive etch-stop 116″ wasformed not only over the thin film resistor 106′, but also continuouslyover a region that does not overlie the thin film resistor 106′. In thisscenario, the electrical conductive etch-stop may also serve as a localinterconnect to other nearby circuit components, subject to designconsiderations. Also in this second alternative method, the metal plug126″ was formed over the region of the etch-stop 116″ that does notoverlie the thin-film resistor 106′. Since in this case the etch-stop116″ is electrically conductive, the metal plug 126″ makes electricalcontact to the thin film resistor 106′ by way of the etch-stop 116″.

FIG. 14 illustrates a cross-sectional view of an exemplary semiconductordevice 100′″ at a step of a third alternative method of forming a thinfilm resistor contact in accordance with the invention. In this thirdalternative method, an electrically insulating etch-stop 116′″ is formedover the thin film resistor 106′, instead of the second dielectric layer110 as described in the previous methods of forming the thin filmresistor contact.

FIG. 15 illustrates a cross-sectional view of an exemplary semiconductordevice 100′″ at a subsequent step of the third alternative method offorming a thin film resistor contact in accordance with the invention.In this subsequent step, the dielectric layer 122′″ is deposited overthe etch-stop layer 116′″.

FIG. 16 illustrates a cross-sectional view of an exemplary semiconductordevice 100′″ after subsequent steps of the third alternative method offorming a thin film resistor contact in accordance with the invention.In this case, a contact opening 124″ is formed through the dielectriclayer 122′″ to expose the underlying etch-stop 116′″ using an etchingprocess that is selective to the etch-stop 116′″. Then, the contactopening 124″ is extended through the etch-stop 116′″ to expose theunderlying thin film resistor 106′ using an etching process that isselective to the thin film resistor 106′. Once the contact opening 124″is formed, a metal plug 128′ is formed within the contact opening 124″.

An advantage of the described methods of forming a thin film resistorcontact of the invention is that the etch-stop allows the resistorcontact opening to be formed by the same dry etching techniques that areused to open up the standard contacts to other components of anintegrated circuit. This is because the etch stop protects theunderlying thin film resistor from erosion which may otherwise occurfrom the dry etching if the etch-stop were not present. Since dryetching is typically anisotropic, the dry etching of the contact openingallows the opening 124′ to be more uniform throughout the wafer and fromwafer-to-wafer. The more controllable contact opening is particularlyuseful when tungsten (W) plugs are used, as it avoids a number ofproblems associated with overetched contact openings, such as incompletefills, excessive removal of the plug due to dishing from the polish, andthe peeling of the plugs due to high tensile stress of tungsten.

In the foregoing specification, the invention has been described withreference to specific embodiments thereof. It will, however, be evidentthat various modifications and changes may be made thereto withoutdeparting from the broader spirit and scope of the invention. Thespecification and drawings are, accordingly, to be regarded in anillustrative rather than a restrictive sense.

It is claimed:
 1. A method of forming a thin film resistor contact,comprising: forming a thin film resistor; forming a first dielectriclayer over said thin film resistor; forming a first opening through saidfirst dielectric layer to expose a first underlying portion of said thinfilm resistor; forming an electrically conductive etch-stop within saidfirst opening of said first dielectric layer; forming a seconddielectric layer over said etch-stop and said first dielectric layer;forming a second opening through said second dielectric layer to exposea second underlying portion of said etch-stop; and forming a metal plugwithin said second contact opening, wherein said metal plug is inelectrical contact with said thin film resistor by way of saidetch-stop.
 2. The method of claim 1, wherein said first and secondopenings vertically overlap.
 3. The method of claim 1, wherein saidfirst and second openings do not vertically overlap.
 4. The method ofclaim 1, wherein said thin film resistor comprises silicon chromium(SiCr).
 5. The method of claim 1, wherein said thin film resistorcomprises nickel chromium (NiCr).
 6. The method of claim 1, wherein saidthin film resistor comprises tantalum nitride (TaN).
 7. The method ofclaim 1, wherein said etch-stop comprises titanium (Ti) andtitanium-nitride (TiN).
 8. The method of claim 1, wherein said etch-stopcomprises titanium-tungsten (TiW) and titanium-tungsten-nitride (TiWN).9. The method of claim 1, wherein forming said second opening throughsaid second dielectric layer comprises dry etching said seconddielectric layer to form said second opening.
 10. The method of claim 1,wherein said metal plug comprises titanium and titanium nitride.
 11. Themethod of claim 1, wherein said metal plug comprises tungsten.
 12. Amethod of forming a thin film resistor contact, comprising: forming athin film resistor; forming a first dielectric layer over said thin filmresistor; forming a first opening through said first dielectric layer toexpose a first underlying portion of said thin film resistor; forming anelectrically insulating etch-stop within said first opening of saidfirst dielectric layer; forming a second dielectric layer over saidetch-stop and said first dielectric layer; forming a second openingthrough said second dielectric layer to expose a second underlyingportion of said etch-stop; removing said etch-stop underlying saidsecond opening; and forming a metal plug within said second contactopening, wherein said metal plug is in direct electrical contact withsaid thin film resistor.
 13. The method of claim 12, wherein said thinfilm resistor comprises silicon chromium (SiCr).
 14. The method of claim12, wherein said thin film resistor comprises nickel chromium (NiCr).15. The method of claim 12, wherein said thin film resistor comprisestantalum nitride (TaN).
 16. The method of claim 12, wherein saidetch-stop comprises silicon oxynitride.
 17. The method of claim 12,wherein said etch-stop comprises silicon nitride.
 18. The method ofclaim 12, wherein forming said second opening through said seconddielectric layer comprises dry etching said second dielectric layer toform said second opening.
 19. The method of claim 12 wherein said metalplug comprises titanium and titanium nitride.
 20. The method of claim12, wherein said metal plug additionally comprises tungsten.